(1) Field of the Invention
The present invention relates to a through type capacitor used for various electric and electronic equipment.
(2) Description of the Prior Art
FIGS. 1a and 1b illustrate a conventional through type capacitor having two capacitor units which is used for a magnetron circuit of a microwave oven or the like. FIG. 1a shows a partial cross section and FIG. 1b an equivalent circuit.
This conventional through type capacitor comprises two capacitor units 2, each having a through hole extending throughout the axial length thereof, through which a through terminal 3 is inserted. Each capacitor unit 2 comprises a cylinder, formed of such a dielectric material as ceramic, having an electrode on both ends thereof. An electrode on one end of the capacitor unit 2 is electrically connected with the through terminal 3, and another electrode on the other end of the capacitor unit 2 is electrically connected with a grounding plate 5. A resin cover 6a is placed around the outer peripheral surface of the capacitor unit 2, and another resin cover 6b is inserted into the grounding plate 5. A resin 7 injected from both ends A and B fills the space. between the resin cover 6 and the capacitor unit 2, in order to securely insulate the electrode on the above other end of the capacitor unit 2 from the through terminal 3.
As shown in FIG. 1b, noise currents i.sub.1 and i.sub.2 flow from the A end of the through terminal 3 and pass from one end of the capacitor unit 2 to the other end, until it is bypassed to the grounding plate 5.
Such noise currents inevitably generate a large residual inductance. Practically, if the through type capacitor has a capacitance of approx. 200 pF, a residual inductance of 7 to 10 nH is generated. With such a capacitor, resonance occurs at around 100 MHz,
15 and an impedance of approx. 30 .OMEGA. is generated at around 500 MHz. The capacitor absorbs a noise current of only up to 300 MHz max., but does not effectively absorb a noise current having a higher frequency.